Model a Java Runtime Engine doing its job

[xxk...@gmail.com]

In UML terms, the Java Runtime Engine seems like an Execution Environment. I'd like to see it modeled as doing its job: namely, "executing" a real-world model of something very simple, such as a T-shirt seller.

I have an idea how to do this but low confidence I'd get it right. I'll be grateful for anyone's thoughts / suggestions / examples. Of course a pointer to somewhere that's already done something of the sort would be great.